The present invention relates to a dispenser for irrigation chemicals. More particularly, the present invention relates to a dispenser for providing water soluble or water-borne chemicals via an irrigation system to the vegetation served thereby.
More particularly, the present invention relates to such a dispenser for irrigation chemicals including a fail-safe antisiphon, or vacuum breaker, valve.
A conventional dispenser for irrigation chemicals is known wherein a cup-like canister is provided which communicates with a water supply pipe of an irrigation system. A single compressed pellet of chemical material is placed into the cup-like canister. When the irrigation system operates, the water flow through the pipe is in part diverted through the canister and carries the chemical material to the vegetation by dissolving or eroding the pellet of chemical material.
While this known conventional irrigation chemical dispenser is inexpensive and simple in construction and use, it also suffers from several deficiencies. For example, because the pellet of chemical material to be inserted into the cup-like canister is available in one size only, the quantity of chemical material dispensed cannot be proportioned according to the area of vegetation or number of plants served by the irrigation system. Possibly, a user of such a dispenser may attain a rough approximation of such proportioning by breaking the pellets into fractions for an irrigation system serving a small vegetation area, or providing multiple dispensers in a system serving a large vegetation area. However, both of these expedients are undesirable, and are inconvenient or expensive.
This known canister-type chemical dispenser is limited in its use to chemicals of solid form which can be compressed into the single pellet for inserting into the canister. While a variety of such pellets are available for grasses, evergreens, roses, etc., the conventional canister-type dispenser cannot use irrigation chemicals of liquid, paste, powder, or granular form.
Another conventional irrigation chemical dispenser is known in accord with U.S. Pat. No. 4,558,715. This teaching is believed to provide a dispenser wherein a drive piston is reciprocated by flowing water under control of a valve device. The drive piston, by its reciprocation, causes reciprocation also of a metering piston. The metering piston draws a selected liquid irrigation chemical from a source thereof and injects the liquid chemical into the water flow downstream of the drive piston.
Unfortunately, the device taught by the '715 patent is both somewhat complex in its construction, and expensive. This device controls the flow of liquid irrigation chemical as a percentage of the total water flow. Such precise control of the percentage of irrigation chemical is believed not to be necessary for an irrigation system to successfully meet the needs of the vegetation served thereby. All that need be effected, in contrast, is control of the total quantity of chemical material dispensed according to the vegetation area or number of plants served by the irrigation system. The device according to the '715 patent is further limited to use of liquid irrigation chemicals.
With all of the conventional irrigation chemical dispensers mentioned above, if a potable water system feeds the irrigation system, the latter must generally include a conventional antisiphon valve as well. Such antisiphon valves are employed to ensure no water from the irrigation system may be drawn back into the potable water supply. Such drawing back of irrigation system water into the potable water supply may occur if a partial vacuum exists in the latter.
A partial vacuum in the potable water supply piping to the irrigation system may result, for example, from maintenance work of the water main feeding the area. When the water main is shut off and opened for maintenance at a level below the branch piping, water in the branch piping runs toward the opening. This flow of water in the branch piping toward the lower opening of the main pipe results in a partial vacuum being created in various parts of the branch piping. Because a branch pipe feeds the irrigation system, the partial vacuum could draw water from the irrigation sysstem into the potable water supply. This back flow water may be laden with bacteria or chemicals from the irrigation system, and may present a health hazard. An antisiphon (or vacuum breaker) valve is used between the irrigation system and the potable water supply to prevent such back flow of water to the potable supply.
While vacuum breaker valves are availble in a variety of designs, a popular type is the pipe applied atmospheric vacuum breaker. This type of vacuum breaker valve includes a housing defining an inlet, an outlet, and a flow path communicating a flow of water between the inlet and outlet. The flow path includes a chamber from which a vent passage opens to ambient. A valve member is movable in the chamber to close the vent passage when water pressure is applied at the inlet. The valve member must open the vent passage when the inlet pressure is atmospheric. Simply stated, the atmospheric vacuum breaker consists of a check valve controlling an air vent that is closed when the device is pressurized and open when the inlet pressure is atmospheric.
In assessing the operating effectiveness of atmospheric vacuum breaker valves, the free water level of the irrigation system is used as a reference level (See, A.S.S.E. Standard No. 1001, Revised: Aug. 1988). This free water level is the highest standing water level which will remain in the irrigation system when pressurized water flow is not being provided. In other words, the irrigation system is considered as a basin having an overflow rim. The height of this rim is the level of water which will remain in the irrigation system. Usually, this free water level for an irrigation system is the grade level of the irrigation water discharge heads. On the other hand, the overflow level of the potable water conduit at the atmospheric vent within the vacuum breaker valve is considered the critical installation level (CIL) for the valve. The vacuum breaker valve must be installed with its CIL a certain distance above the free water level of the irrigation system. In order to assess the effectiveness of the vacuum breaker valve, an intentional fault is introduced into the valve to communicate to the outlet a vacuum applied to the inlet of the valve. The vacuum might undesirably draw water up the outlet toward the inlet. The atmospheric venting effected by the valve must be sufficient to prevent water being drawn into the outlet above a set level. Usually, the height of the CIL above the free water level is six inches, and the highest allowed draw back height is three inches. Thus, the conventional vacuum breaker valve is required to provide a safety factor of two with respect to effective vacuum venting and water draw back at the outlet of the valve.
Unfortunately, when a conventional vacuum breaker valve is employed in combination with a conventional irrigation chemical dispenser, the dispenser might be required to be located a considerable distance below the vacuum breaker valve to insure no irrigation chemical is drawn into the valve. This necessary vertical separation with conventional dispensers and vacuum breaker valves undesirably increases the space required for the plumbing installation.